Analyte Detection Meter and Associated Method of Use

ABSTRACT

A method for obtaining information encoded on an electrochemical test strip is provided. The test strip has two electrodes disposed within a sample space and the information is encoded on the test strip prior to introduction of liquid sample. The method includes the step of introducing sample to the sample space so that the sample is in contact with the two electrodes within the sample space. In another step a value is determined that is representative of the double layer capacitance of the test strip and/or the equivalent capacitance of the test strip. The determined value is then translated into information reflecting a characteristic of the test strip prior to introduction of sample.

BACKGROUND OF THE INVENTION

This application relates to methods for encoding information on anelectrochemical test strip as well as methods for, and meters capableof, obtaining information encoded on a test strip.

Small disposable electrochemical test strips are frequently used in themonitoring of blood glucose by diabetics. Such test strips can also beemployed in the detection of other physiological chemicals of interestand substances of abuse. In general, the test strip comprises at leasttwo electrodes and appropriate reagents for the test to be performed,and is manufactured as a single use, disposable element. The test stripis combined with a sample such as blood, saliva or urine before or afterinsertion in a reusable meter, which contains the mechanisms fordetecting and processing an electrochemical signal from the test stripinto an indication of the presence/absence or quantity of the analytedetermined by the test strip.

Electrochemical test meters are known in the art, for example for thedetermination of blood glucose levels. See, for example, U.S. Pat. Nos.7,771,583; 7,645,374; 7,601,249; 7,547,382; 7,517,439; 7,501,052;7,344,626; 7,090,764; 6,662,439; 6,284,125; 6,071,391; 5,942,102;5,352,2,351; and 5,243,516, all of which are incorporated herein byreference.

Test strips often have information associated with them, such as, interalia, calibration information, regional or country coding, productidentification, customer identification, assay type (e.g. glucose teststrip or ketone test strip), and date of manufacture. PCT PatentApplication Ser. No. PCT/US11/51983 and U.S. Pat. Nos. 7,713,392;7,695,608; 7,645,421; 7,625,473; 7,601,299; and 4,714,874, which areincorporated herein by reference, provide strips with this, and othertypes of information, encoded onto the test strip and associated metersand methods for decoding the information from the strip. The challengefor manufacturers is how to encode information on a test strip and howto obtain the coded information in a manner that is cost effective,reliable, safe, and robust. The present invention provides systems andmethods to solve these difficulties.

SUMMARY OF THE INVENTION

The present invention provides methods for encoding information on to atest strip as well as methods for, and meters capable of, obtaining theinformation encoded on an electrochemical test strip. The methods ofobtaining the information employ the steps of determining a valueindicative of the double layer capacitance or the equivalent capacitanceof the test strip after sample introduction. This value can then betranslated into information regarding a characteristic of the teststrip, which is encoded on the test strip prior to sample introduction.

The present Inventors have found that a strip's double layer and/orequivalent capacitance is a variable that can be controlled/altered soas to encode information on to the test strip. Furthermore, the presentInventor's have found that determining a value indicative of the strip'sdouble layer capacitance or equivalent capacitance when sample ispresent in the sample space and subsequently translating this value intoinformation reflecting a characteristic of the test strip prior tointroduction of sample allows for obtaining the information. The encodedinformation then can be used in a subsequent analysis or correction stepto adjust a calculated value (e.g. value obtained in a determination ordetection of analyte) or it can be used to generate and/or display anerror result or message to a user.

In a first aspect of the present invention, a method for obtaininginformation encoded on an electrochemical test strip having at least twoelectrodes within a sample space is provided. The information is encodedon the strip prior to introduction of sample. The method comprises thesteps of:

-   -   (a) introducing sample to the a sample space so that the sample        is in contact with two electrodes within the sample space;    -   (b) determining a value that is representative of the double        layer capacitance or the equivalent capacitance of the test        strip; and    -   (c) translating the value determined in step (b) into        information reflecting a characteristic of the test strip prior        to introduction of sample;        thereby obtaining information encoded on the electrochemical        test strip.

In a second aspect of the present invention, a method for detecting ananalyte in a sample in contact with two electrodes within a sample spaceof an electrochemical test strip is provided. The test strip hascharacteristic information encoded thereon prior to introduction of asample.

The method comprises the steps of:

-   -   (a) introducing sample to the sample space so that the sample is        in contact with two electrodes within the sample space;    -   (b) determining a value that is representative of the double        layer capacitance or the equivalent capacitance of the test        strip; and    -   (c) translating the value determined in step (b) into        information reflecting a characteristic of the test strip prior        to introduction of sample,    -   (d) detecting analyte in the sample disposed within the sample        space, and    -   (e) using the characteristic information translated in step (c)        to modify a result of step (d).

The invention also provides a meter for receiving an electrochemicaltest strip having electrodes and providing a determination of an analytein a sample applied to the electrochemical test strip when received inthe meter. The meter comprises:

(a) a housing having an opening for receiving an electrochemical teststrip, said test strip having characteristic information encodedthereon;

(b) communications means for receiving input from and communicating aresult to a user; and

(c) circuitry for making a determination of double layer capacitance orequivalent capacitance on a test strip having two electrodes within asample space containing sample received within the meter; circuitry fortranslating the determined double layer capacitance or equivalentcapacitance into information reflecting a characteristic of the teststrip prior to introduction of sample; and circuitry for determinationof an analyte in a sample within the sample space of the test strip.

In a further aspect of the present invention a measurement system isprovided. The system comprises a meter, as described above, and a teststrip having two electrodes within a sample space, wherein the teststrip is disposed within the slot of the housing of the meter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing steps of an embodiment of the presentinvention.

FIGS. 2-6 show different lookup tables containing capacitance values andassociated characteristic information.

FIG. 7 shows an external view of a meter in accordance with theinvention.

DETAILED DESCRIPTION OF THE INVENTION

When a sample space of a test strip is filled with sample, oralternatively when the entirety of the electrodes (or dominantelectrode) within the sample space are covered with sample, then adetermination of a value representative of the test strip's double layercapacitance or equivalent capacitance can be translated intocharacteristic information encoded on the test strip prior to sampleintroduction. Information can be encoded on a test strip by alteringvariables within the sample space which impact the strip's equivalentand/or double layer capacitance when sample covers the electrodes in thesample space. These variables include: controlling or altering theeffective area of the electrodes within the sample space of the teststrip; controlling or altering the material of construction of theelectrodes; electrode surface modification; controlling or altering thetype or concentration of ions (e.g. type and amount of ions such asthose present as salts in the reagent); controlling or altering the typeor concentration of mediator.

DEFINITIONS

As used in the specification and claims of this application, thefollowing definitions should be applied:

(a) “analyte” refers to a material of interest that may be present in asample. In the present application, the examples use glucose as ananalyte, but the present invention is independent of both the type andamount of analyte. Accordingly, application to glucose detection systemsshould be viewed as merely a specific and non-limiting embodiment.

(b) “determination of an analyte” refers to qualitative,semi-quantitative and quantitative processes for evaluating a sample. Ina qualitative evaluation, a result indicates whether or not analyte wasdetected in the sample. In a semi-quantitative evaluation, the resultindicates whether or not analyte is present above some pre-definedthreshold. In a quantitative evaluation, the result is a numericalindication of the amount of analyte present.

(c) “double layer” refers to the charged layers which form at aconductor/electrolyte interface as a result of adsorption of ions on theconductor surface causing a localized layer of neutralizing mirrorcharges in the conductor to form near the solid surface. The doublelayer is formed at each electrode in an electrochemical test strip whena liquid sample is present in contact with the electrode, whether or nota potential is applied. The amount of charge in a double layer, however,is a function of the electrode potential. The double layer structurebehaves essentially as a capacitor.

(d) “double layer capacitance” is the capacitance of a double layer. Itmay be an integral capacitance, in which case it can be represented bythe formula C_(int)=IΔt/ΔV or a differential capacitance, in which caseit can be represented by the formula C_(dif)=I/(dV/dt), where I iscurrent, t is time and V is voltage. As described in Harding (U.S. Pat.No. 7,547,382), in some instances the measured double layer capacitancecan be dominated by one electrode, for example, if one electrode has asubstantially larger area, or where the adsorption of ions of one chargeis stronger than ions of the other charge in the sample. Double layercapacitance measured in these instances is within the scope of theinvention, although care should be taken where one electrode is dominantthat the geometry of filling is such that the double layer capacitanceof the dominant electrode is representative of the fill-state of theelectrochemical strip. Where double layer capacitance of a test strip isdetermined, it is preferably determined in accordance with the teachingsof U.S. Pat. No. 7,547,382, to Harding et. al which is incorporatedherein by reference for all purposes.

(e) “double layer charging” is the process of increasing the chargestored in a double layer as a result of an applied potential. The phrase“double layer charging at the electrodes” refer to charging at bothelectrodes or at a dominant electrode.

(f) “double layer discharging” is the process of decreasing the chargestored in a double layer as a result of switching off an appliedpotential. The phrase “double layer discharging at the electrodes” referto discharging at both electrodes or at a dominant electrode.

(g) “equivalent capacitance” is herein understood to mean the totalequivalent capacitance between the electrodes (e.g. across the samplespace electrochemical test strip, when electrodes are in contact withsample in the sample space) when potential is applied between theelectrodes. The “equivalent capacitance” of the test strip is acombination of the strip's double layer capacitance and the strip'sFaradaic capacitance. Where equivalent capacitance is determined, it ispreferably determined in accordance with the teachings in either or bothof U.S. Pat. No. 6,872,298 and/or U.S. patent application Ser. No.09/974,597 (Published as US 2003/0098233).

(h) “Faradaic capacitance” as used herein refers to thepseudo-capacitance component of the test strip's equivalent capacitanceand is representative of the electrochemical reaction process thatoccurs on the electrode surface.

(i)“electrochemical test strip” or simply “test strip” refers to a striphaving at least two electrodes within a sample space, and any necessaryreagents for determination of an analyte in a sample placed between theelectrodes. In preferred embodiments, the electrochemical test strip isdisposable after a single use, and has electrical connectors forattachment to a separate and reusable meter that contains theelectronics for applying potential, analyzing signals and displaying aresult. In another embodiment, the electrochemical test strip includesmultiple sample spaces and electrodes disposed within those samplespaces. In this later embodiment, the “test strip” can be used multipletimes where sample is introduced to one or more at the sample spaces atdifferent times.

(j) “facing electrodes” are a pair of electrodes disposed parallel tobut in a separate plane from each other. Some or all of the opposedsurfaces of a pair of facing electrodes preferably overlap, such thatpotential gradients and current flows between the electrodes are in adirection substantially perpendicular to the opposed surfaces. Facingelectrodes are distinguished from side-by-side electrodes in which thetwo electrode surfaces lie in the same plane, and in which potentialgradients and current flow is substantially parallel to the surface ofthe electrodes. The present invention can be used with either facing orside-by-side electrodes, as well as other geometric arrangements.

(k) “information encoded on a test strip” is any type of informationwhich details a characteristic of the test strip that is intentionally,unintentionally, or inherently encoded on a test strip duringmanufacture or otherwise prior to introduction of a sample to beanalyzed. The information is encoded on the test strip prior tointroduction of sample to the sample space. Information can be encodedon a test strip by altering variables within the sample space whichimpact the strip's equivalent and/or double layer capacitance whensample covers the electrodes in the sample space. These variablesinclude: controlling or altering the effective area of the electrodeswithin the sample space of the test strip; controlling or altering thematerial of construction of the electrodes; electrode surfacemodification; controlling or altering the type or concentration of ions(e.g. type and amount of ions such as those present as salts in thereagent); controlling or altering the type or concentration of mediator.Encoding information to the test strip for example can be accomplishedby forming electrode(s) within the sample space having specifiedeffective areas during manufacture or can be accomplished as a postproduction step by altering the effective area of the electrode(s)within the sample space by etching, punching, ablating, scoring, orotherwise removing conductive material from the electrode within thesample space. A non-limiting exemplary list of the type ofcharacteristic information capable of being encoded on a test stripincludes: calibration information, regional or country coding, productidentification, customer identification, assay type (e.g. glucose teststrip or ketone test strip), and date of manufacture.

(l) “obtaining information” is herein understood to mean decoding,reading, translating, retrieving, or otherwise obtaining orascertaining, the information encoded on the test strip.

(m) “translating” is herein understood to mean using a value determinedin one set of steps to provide information about the test strip which isrepresentative of a characteristic of the test strip prior tointroduction of sample to the test strip. For example, the determinedvalue which is representative of the double layer capacitance orequivalent capacitance of a test strip, can be reconciled with a lookuptable stored in a meter or obtained by a meter. The lookup table canhave a range, or ranges, of values which are indicative of variouscharacteristic information of the test strip.

(n) “value representative of double layer capacitance or equivalentcapacitance” is herein understood to mean the actual determinedcapacitance or a separate value which comprises information about thecapacitance of the strip (e.g. an electrical signal or some othervalue).

(o) “effective area of an electrode” is herein understood to mean theconductive portion of an electrode, or the dominant electrode, which isin contact with sample in the sample space and capable of beingelectrically connected with a meter. The “effective area” includesconductive portions of the electrode which are exposed to sample whenpresent in the sample space. The “effective area” includes theconductive portions which are exposed to sample which lie within the twodimensional planar footprint (e.g. length, width, radius, etc.) as wellas conductive portions of the electrode which are exposed to samplewhich lie within a third dimension (e.g. depth or thickness) such aslocated in pits, crevices, and/or pores of the electrode.

Reference throughout the specification to “one embodiment,” “anotherembodiment,” “an embodiment,” “some embodiments,” and so forth, meansthat a particular element (e.g., feature, structure, property, and/orcharacteristic) described in connection with the embodiment is includedin at least one embodiment described herein, and may or may not bepresent in other embodiments. In addition, it is to be understood thatthe described element(s) may be combined in any suitable manner in thevarious embodiments.

Method of Obtaining Encoded Information from a Test Strip:

In a first aspect, the present invention provides a method for obtaininginformation encoded on an electrochemical test strip. The test strip hasat least two electrodes disposed within a sample space and theinformation is encoded on the test strip prior to introduction of liquidsample. As shown in FIG. 1, the method comprises the steps of:

-   -   (a) introducing sample to the sample space so that the sample is        in contact with two electrodes within the sample space;    -   (b) determining a value that is representative of the double        layer capacitance (DLC) or the equivalent capacitance (EC) of        the test strip; and    -   (c) translating the value determined in step (b) into        information reflecting a characteristic of the test strip prior        to introduction of sample;        thereby obtaining information encoded on the electrochemical        test strip.

The step of (b) determining a value that is representative of the doublelayer capacitance or the equivalent capacitance of the test strip, isknown in the art and is not particularly limited herein. The determinedvalue may be the actual value of the test strip's double layercapacitance or its equivalent capacitance, or it may be a value orsignal that is representative of either of both of these capacitancevalues.

Prior art references discussed herein make use of a test strip's doublelayer capacitance or equivalent capacitance in determining whether asufficient amount of sample has been applied to and is disposed with thesample space to perform an electrochemical determination of analyte. Inthese references, it is disclosed that sample volume can be determinedas a function of the area of the electrode(s) wetted by sample and thethickness of a spacer layer and/or separation of electrodes. Thesereferences each describe and employ different capacitance-determiningmethods for determining the sample-wetted electrode area within thesample space and hence provide different methods of determining samplesufficiency within the sample space. Any of these methods fordetermining double layer capacitance or equivalent capacitance can beemployed to accomplish step (b) of the present invention.

For example, U.S. Pat. No. 7,547,382, to Harding et. al, which isincorporated herein by reference, discloses several different methodsfor measuring a test strip's double layer capacitance. Harding uses ameasure of the strip's double layer capacitance in a determination ofwhether sufficient sample is present within the sample space to performan electrochemical determination of analyte within the sample.

Harding describes that the double layer capacitance of a test strip withsample in the sample space can be determined using the steps of:

-   -   (i) applying a potential difference between the electrodes of        the test strip;    -   (ii) switching off the applied potential and optionally        reapplying a second potential;    -   (iii) observing current generated and determining from the        observed current a double layer charging or discharging at the        electrodes; and    -   (iv) observing a voltage change after the applied potential is        switched off, and    -   (v) determining the double layer capacitance of the test strip        from the measured double layer charging or discharging and the        observed voltage change.        Harding employs these steps to determine double layer        capacitance of the test strip which is either the integral        capacitance or differential capacitance of the test strip.

Where a value representative of the equivalent capacitance of the teststrip is determined, it can be determined in accordance with theteachings in either or both of U.S. Pat. No. 6,872,298 and/or U.S.patent application Ser. No. 09/974,597 (Published as US 2003/0098233),both of which list Kermani as an Inventor and are incorporated herein byreference. In these references, Kermani makes use of a test strip'sequivalent capacitance when sample is present within the sample space inthe determination of whether sufficient sample is present within thesample space to perform an electrochemical determination of analytewithin the sample. In US 2003/0098233, Kermani describes a method ofdetermining a test strip's equivalent capacity, includes the steps of:

-   -   (i) applying an alternating voltage having a selected amplitude        and a selected frequency between the electrodes of the test        strip;    -   (ii) measuring the current generated from the application of        potential in step (I); and    -   (iii) determining the equivalent capacitance of the test strip        from the current measured in step (ii), wherein the equivalent        capacitance includes both the double layer capacitance and the        Faradaic capacitance of the test strip.        In Kermani's U.S. Pat. No. 6,872,298, he describes another        method of determining a test strip's equivalent capacity        includes the steps of:

(i) applying a potential difference between the electrodes of the teststrip thereby charging the test strip, wherein a double layercapacitance is created within the test strip and a voltage is generatedby charging the test strip;

(ii) converting the voltage created by charging the test strip to anoscillating voltage having a period proportional to the created doublelayer capacitance;

(iii) observing the oscillating voltage; and

(iv) determining the equivalent capacitance of test strip from theobserved oscillating voltage.

As discussed above, step (b) can be suitably accomplished using theteachings of the prior art and is not particularly limited herein.

To obtain the most accurate (b) determination of a value representativeof the strip's double layer capacitance or equivalent capacitance forthe purposes of obtaining information encoded on the test strip prior tointroduction of sample, the sample space will be preferably completelyfilled with sample. For example, it is preferred that sample is disposedbetween and completely covering the electrodes (or dominant electrode).This may mean the sample space is completely filled with sample or thismay mean that the sample space is not entirely filled with sample, butthat sample covers the electrodes. In preferred embodiment the methods,strips, meters, and meter/strip combinations of the present inventionfurther comprise structures or functionality to determine whether samplecompletely covers the electrodes (or dominant electrode) within thesample space. This step can occur at any time after introduction ofsample, however as shown in FIG. 1 this preferably occurs prior to thedetermination of the strip's capacitance value. Methods and apparatusesuseful for fill detection are well-known in the art and are notparticularly limited herein. For example, U.S. Pat. No. 4,929,426discloses the use of an impedance electrode that sample flows over whenthe sample chamber is filled, while U.S. Pat. No. 5,582,697, U.S. Pat.No. 6,212,417, and U.S. Pat. No. 6,299,757, all of which areincorporated by reference, disclose the use of a third electrode thatcan be used for fill detection. U.S. Pat. No. 6,743,635, which isincorporated by reference, discloses a four electrodes approach,including separate fill detect anode and cathode. U.S. Pat. No.5,997,817, which is incorporated by reference, discloses a test stripwith a window through which the sample can be viewed, and a“fill-to-here” line to assess sample sufficiency.

Once the value representative of a test strip's double layer capacitanceor equivalent capacitance is determined, this value can be (c)translated into information reflecting a characteristic of the teststrip prior to introduction of sample. As shown in FIGS. 2 and 3, thetranslation step is preferably a reconciliation (e.g. referencing) ofthe determined double layer capacitance or equivalent capacitance of thetest strip with a lookup table. In FIG. 2 the lookup table correlatesranges of capacitance values with regional identification or countrycoding of the test strips. In FIG. 3, the lookup table correlates rangesof capacitance values with the type of analyte the test strip isdesigned to measure. In FIG. 4, the lookup table correlates ranges ofcapacitance values with calibration information of the test strip. InFIG. 5, the lookup table correlates ranges of capacitance values withproduct identification of the test strip. In FIG. 6, the lookup tablecorrelates ranges of capacitance values with a production or expirationyear.

Translating the value of the strip's double layer capacitance orequivalent capacitance into information reflective of a characteristicof the test strip prior to introduction of sample, allows for obtaininguseful characteristic information of the test strip. As shown in FIG. 1,in preferred embodiments, the obtained information causes, or is usedin, a subsequent action or step. In some embodiments the subsequentaction or step is to generate or otherwise cause display of an errorresult, or error message, which indicates that the test strip is notsuitable for use with the meter, or that some other error has occurred.In other embodiments, the subsequent action or step is one where theobtained or translated information is used in a subsequent measurementor analyte determination step or to modify a result from a subsequentmeasurement or analyte determination step.

Encoding Information on a Test Strip.

Information can be encoded on a test strip by altering variables withinthe sample space which impact the strip's equivalent and/or double layercapacitance when sample covers the electrodes in the sample space. Thesevariables include: controlling or altering the effective area of theelectrodes within the sample space of the test strip; controlling oraltering the material of construction of the electrodes; electrodesurface modification; controlling or altering the type or concentrationof ions (e.g. type and amount of ions such as those present as salts inthe reagent); controlling or altering the type or concentration ofmediator.

For example in one embodiment when information is to be encoded on atest strip, the effective electrode area may be altered or formed byincreasing or decreasing its two-dimensional conductive surface areafootprint (e.g. to increase/decrease length, width or radius, etc.) incontact with the sample. Alternatively, or in combination withcontrolling to two-dimensional surface area footprint, a thirdconductive dimension of the electrode can be altered/controlled byincreasing/decreasing the thickness of the electrode (e.g. where theelectrode has a pitted or porous surface which provides a thirddimension of sample contact). In other embodiments, the type and/orconcentration of mediator and or ions (e.g. salts) present in a reagentdisposed within the sample space may be altered to encode information tothe test strip, which in turn will alter the strip's double layer and/orequivalent capacitance which allows for translation and obtaining of theinformation according to the herein described methods.

Determination of an Analyte, for Example Glucose

The methods of the present invention are preferably combined with asubroutine directed to the detection and/or determination of analyte inthe sample. The detection and/or determination of analyte subroutine canoccur prior to, during, or after obtaining the encoded information fromthe test strip. In some embodiments, the subroutine of performing and/orthe result of the detection and/or determination of analyte is adjustedor corrected depending on the type and content of information obtainedfrom the test strip. In other embodiments the subroutine of detectionand/or determination steps is halted, or not performed, depending on thetype and content of information obtained from the test strip. In yetother embodiments just a error message is displayed to a user dependingon the characteristic obtained from and encoded on the test strip.

Subroutines for the electrochemical detection and determination of ananalytes such as glucose are conventionally achieved by applying apotential to an electrochemical cell containing a sample to be evaluatedfor the presence/amount of glucose, an enzyme that oxidizes or reducesglucose, such as glucose oxidase, dehydrogenase, or reductase, and aredox mediator. Reduced mediator is oxidized at one of the electrodes,and electrochemical balance is maintained by a reducing reaction at theother electrode to result in a measurable current. The measured currentis related to the concentration of glucose in the sample, and varioustechniques are known for determining glucose concentrations in such asystem. (See, for example, U.S. Pat. Nos. 6,284,125; 5,942,102;5,352,2,351; and 5,243,516, which are incorporated herein by reference.)

Determination of glucose or other analytes in a sample can also be madeusing other electrochemical techniques. These include potentiometry, forexample as described in U.S. Pat. No. 6,251,260, which is incorporatedherein by reference, or coulometry, for example as described in U.S.Pat. No. 6,299,757 which is incorporated herein by reference.

In one embodiment, a method for determining analyte in a sample incontact with two electrodes within a sample space of an electrochemicaltest strip is provided. The test strip has characteristic informationencoded thereon prior to introduction of a sample. The method comprisesthe steps of:

-   -   (a) introducing sample to the sample space so that the sample is        in contact with two electrodes within the sample space;    -   (b) determining a value that is representative of the double        layer capacitance or the equivalent capacitance of the test        strip; and    -   (c) translating the value determined in step (b) into        information reflecting a characteristic of the test strip prior        to introduction of sample,    -   (d) determining analyte in the sample disposed within the sample        space, and    -   (e) using the characteristic information translated in step (c)        to modify a result of step (d).

Step (c) occurs after step (b), however step (d) can occur before orafter either of steps (b) or (c).

Apparatus of the Invention

The method of the invention can be used with any strip that has at leasttwo electrodes provided a meter apparatus can receive the strip andprovide the necessary applications of voltage and signal processing.Such a meter also forms an aspect of the present invention. Thus, theinvention provides a meter for receiving an electrochemical test striphaving electrodes and providing a determination of an analyte in asample applied to the electrochemical test strip when received in themeter, said meter comprising:

(a) a housing having an opening for receiving an electrochemical teststrip, said test strip having characteristic information encodedthereon;

(b) communications means for communicating a result to a user; and

(c) circuitry and a processor for making a determination of double layercapacitance or equivalent capacitance on a test strip having twoelectrodes within a sample space containing sample received within themeter; circuitry and a processor for translating the determined doublelayer capacitance or equivalent capacitance into information reflectinga characteristic of the test strip prior to introduction of sample; andcircuitry and a processor for determination of an analyte in a samplewithin the sample space of the test strip.

FIG. 7 shows an external view of a meter in accordance with theinvention. The meter has a housing 61, and a display 62. The housing 61has an opening 63, into which a test strip is inserted for use. Themeter may also have a button 64 for signaling the start of themeasurement cycle, or may have an internal mechanism for detecting theinsertion of a test strip and/or the application of a sample. Suchmechanisms are known in the art, for example from U.S. Pat. Nos.5,266,179; 5,320,732; 5,438,271 and 6,616,819, which are incorporatedherein by reference.

In the meter of the invention, buttons, displays such as LCD displays,RF, infrared or other wireless transmitters, wire connectors such asUSB, parallel or serial connections constitute means for receiving inputfrom and communicating a result to a user, and can be used individuallyand in various combinations.

The meter of the present invention includes circuitry in the form ofprocessor(s), software, and/or firmware, or any other type ofinstructions or circuitry capable of carrying out the method stepsdescribed above.

EXAMPLES Obtaining Information from Test Strips Example 1

An electrochemical meter is configured to determine the double layercapacitance of a test strip disposed within its test strip port. Acontrol solution sample is introduced to two different test stripshaving different information encoded thereon as a result of havingdifferent effective electrode areas (e.g. strip 1—information 1/strip2—information 2). It is determined that the control solution filled andsample space and completely covers two electrodes within the samplespace. The double layer capacitance of both strips is determined andyield different values. These determined values are then translated(e.g. via reconciliation with a lookup table with known double layercapacitance ranges identifying the characteristic information) and theinformation encoded on the strips is determined to be strip1—information 1/strip 2—information 2.

Obtaining Information from Test Strips Example 2

An electrochemical meter is configured to determine the equivalentcapacitance of a test strip disposed within its test strip port. Acontrol solution sample is introduced to two different test stripshaving different information encoded thereon as a result of havingdifferent ionic salts present in the sample space (e.g. strip1—potassium—information 1/strip 2—sodium—information 2). It is thendetermined that the control solution filled and sample space andcompletely covers two electrodes within the sample space. The equivalentcapacitance of both strips is then determined and yields differentvalues. These determined values are then translated (e.g. viareconciliation with a lookup table with known equivalent capacitanceranges with characteristic information) and the information encoded onthe strips is determined to be strip 1—information 1/strip 2—information2.

1. A method for obtaining characteristic information encoded on anelectrochemical test strip having two electrodes disposed within asample space, wherein the characteristic information is encoded on thetest strip prior to introduction of sample, the method comprising thesteps of: (a) introducing sample to the sample space so that the sampleis in contact with two electrodes within the sample space; (b)determining a value that is representative of the double layercapacitance or the equivalent capacitance of the test strip; and (c)translating the value determined in step (b) into information reflectinga characteristic of the test strip prior to introduction of sample;thereby obtaining information encoded on the electrochemical test strip.2. The method of claim 1, further comprising the step performed afterstep (a) of determining whether sample completely covers the electrodeswithin the sample space.
 3. The method of claim 1, where step (b) isperformed using the steps of: (i) applying a potential differencebetween the electrodes of the test strip; (ii) switching off the appliedpotential and optionally reapplying a second potential; (iii) observingcurrent generated and determining from the observed current a doublelayer charging or discharging at the electrodes; and (iv) observing avoltage change after the applied potential is switched off, and (v)determining the double layer capacitance of the test strip from themeasured double layer charging or discharging and the observed voltagechange.
 4. The method of claim 1, where step (b) is performed using thesteps of: (i) applying an alternating voltage having a selectedamplitude and a selected frequency between the electrodes of the teststrip; (ii) measuring the current generated from the application ofpotential in step (I); and (iii) determining the equivalent capacitanceof the test strip from the current measured in step (ii), wherein theequivalent capacitance includes both the double layer capacitance andthe Faradaic capacitance of the test strip.
 5. The method of claim 1,where step (b) is performed using the steps of: (i) applying a potentialdifference between the electrodes of the test strip thereby charging thetest strip, wherein a double layer capacitance is created within thetest strip and a voltage is generated by charging the test strip; (ii)converting the voltage created by charging the test strip to anoscillating voltage having a period proportional to the created doublelayer capacitance; and (iii) observing the oscillating voltage; and (iv)determining the equivalent capacitance of test strip from the observedoscillating voltage.
 6. The method of claim 1, wherein thecharacteristic information encoded on the strip is selected from thegroup consisting of: calibration information, regional or countrycoding, product identification, customer identification, assay type, anddate of manufacture.
 7. The method of claim 1, wherein the methodfurther comprises the step of: (d) performing an action based upon thecharacteristic information translated in step (c).
 8. The method ofclaim 7, wherein the action performed based upon the characteristicinformation determined in step (c) is modifying a calculation.
 9. Themethod of claim 7, wherein the action performed based upon thecharacteristic information determined in step (c) is displaying an errormessage to a user.
 10. A method for determining analyte in a sample incontact with two electrodes within a sample space of an electrochemicaltest strip, wherein the test strip has characteristic informationencoded thereon prior to introduction of a sample, the method comprisingthe steps of: (a) introducing sample to the sample space so that thesample is in contact with two electrodes within the sample space; (b)determining a value that is representative of the double layercapacitance or the equivalent capacitance of the test strip; and (c)translating the value determined in step (b) into information reflectinga characteristic of the test strip prior to introduction of sample, (d)determining analyte in the sample disposed within the sample space, and(e) using the characteristic information translated in step (c) tomodify a result of step (d).
 11. The method of claim 10, furthercomprising the step performed after step (a) of determining whethersample completely covers the electrodes within the sample space.
 12. Themethod of claim 10, where step (b) is performed using the steps of: (i)applying a potential difference between the electrodes of the teststrip; (ii) switching off the applied potential and optionallyreapplying a second potential; (iii) observing current generated anddetermining from the observed current a double layer charging ordischarging at the electrodes; and (iv) observing a voltage change afterthe applied potential is switched off, and (v) determining the doublelayer capacitance of the test strip from the measured double layercharging or discharging and the observed voltage change.
 13. The methodof claim 10, where step (b) is performed using the steps of: (i)applying an alternating voltage having a selected amplitude and aselected frequency between the electrodes of the test strip; (ii)measuring the current generated from the application of potential instep (I); and (iii) determining the equivalent capacitance of the teststrip from the current measured in step (ii), wherein the equivalentcapacitance includes both the double layer capacitance and the Faradaiccapacitance of the test strip.
 14. The method of claim 10, where step(b) is performed using the steps of: (i) applying a potential differencebetween the electrodes of the test strip thereby charging the teststrip, wherein a double layer capacitance is created within the teststrip and a voltage is generated by charging the test strip; (ii)converting the voltage created by charging the test strip to anoscillating voltage having a period proportional to the created doublelayer capacitance; and (iii) observing the oscillating voltage; and (iv)determining the equivalent capacitance of test strip from the observedoscillating voltage.
 15. The method of claim 10, wherein thecharacteristic information encoded on the strip is selected from thegroup consisting of: calibration information, regional or countrycoding, product identification, customer identification, assay type, anddate of manufacture.
 16. A meter for receiving an electrochemical teststrip having electrodes and providing a determination of an analyte in asample applied to the electrochemical test strip when received in themeter, said meter comprising: (a) a housing having an opening forreceiving an electrochemical test strip, said test strip havingcharacteristic information encoded thereon; (b) communications means forcommunicating a result to a user; and (c) circuitry and a processor formaking a determination of double layer capacitance or equivalentcapacitance on a test strip having two electrodes within a sample spacecontaining sample received within the meter; circuitry and a processorfor translating the determined double layer capacitance or equivalentcapacitance into information reflecting a characteristic of the teststrip prior to introduction of sample; and circuitry and a processor fordetermination of an analyte in a sample within the sample space of thetest strip.
 17. The meter of claim 16, further comprising circuitry formaking a determination of whether sample completely covers theelectrodes within the sample space.
 18. The meter of claim 16, whereinthe circuitry for making a determination of double layer capacitance orequivalent capacitance comprises a processor and software which performthe steps of: (i) applying a potential difference between the electrodesof the test strip; (ii) switching off the applied potential andoptionally reapplying a second potential; (iii) observing currentgenerated and determining from the observed current a double layercharging or discharging at the electrodes; and (iv) observing a voltagechange after the applied potential is switched off, and (v) determiningthe double layer capacitance of the test strip from the measured doublelayer charging or discharging and the observed voltage change.
 19. Themeter of claim 16, wherein the circuitry for making a determination ofdouble layer capacitance or equivalent capacitance comprises a processorand software which perform the steps of: applying an alternating voltagehaving a selected amplitude and a selected frequency between theelectrodes of the test strip; (ii) measuring the current generated fromthe application of potential in step (I); and (iii) determining theequivalent capacitance of the test strip from the current measured instep (ii), wherein the equivalent capacitance includes both the doublelayer capacitance and the Faradaic capacitance of the test strip. 20.The meter of claim 16, wherein the circuitry for making a determinationof double layer capacitance or equivalent capacitance comprises aprocessor and software which perform the steps of: (i) applying apotential difference between the electrodes of the test strip therebycharging the test strip, wherein a double layer capacitance is createdwithin the test strip and a voltage is generated by charging the teststrip; (ii) converting the voltage created by charging the test strip toan oscillating voltage having a period proportional to the createddouble layer capacitance; and (iii) observing the oscillating voltage;and (iv) determining the equivalent capacitance of test strip from theobserved oscillating voltage.
 21. The meter of claim 16, wherein theinformation reflecting a characteristic of the test strip prior tointroduction of sample is selected from the group consisting of:calibration information, regional or country coding, productidentification, customer identification, assay type, and date ofmanufacture.
 22. The meter of claim 16, wherein the meter furthercomprises circuitry for: (d) performing an action based upon thecharacteristic information translated in step (c).
 23. The meter ofclaim 22, wherein the action performed based upon the characteristicinformation determined in step (c) is modifying determination of ananalyte.
 24. The method of claim 22, wherein the action performed basedupon the characteristic information determined in step (c) is generatingand displaying an error message to a user.
 25. A measurement systemcomprising a meter in accordance with claim 16 and a test strip havingtwo electrodes within a sample space, wherein the test strip is receivedwithin the opening in the housing of the meter.
 26. The measurementsystem of claim 25, wherein the test strip measures glucose in a sample.